In a linear radio communication system, the peak-to-average ratio (i.e., the ratio of the signal envelope to the average power of the signal) of a communication signal is of critical importance to the cost, complexity, and size of the radio's linear power amplification system. Seemingly small reductions in peak-to-average ratio can have a significant impact on each of the above-mentioned system characteristics. This is especially true for systems that require high output power, such as a base station.
A problem in the design of linear power amplifiers is the effect of the transmitted signal's peak-to-average ratio on performance. As the peak-to-average ratio (PAR) increases, the attenuation needed for adequate splatter performance of the power amplifier increases proportionally. Therefore, it is highly desirable to control the PAR of the signal input to the amplifier. However, any attempt to reduce the nominal PAR through other than linear processing functions (i.e., non-linear signal processing) generates splatter. Splatter, which is signal energy that extends beyond the frequency band allocated to a signal, is highly undesirable because it interferes with communications on adjacent channels.
One method of reducing PAR is hard clipping, which reduces each signal value exceeding a clip threshold to a predetermined magnitude, often the threshold magnitude. Hard-clipping causes significant splatter due to the abrupt nature of its operation.
Another method of reducing PAR is a "soft" algorithm that applies the desired signal to a non-linear device that limits signal peaks. A significant proportion of the input samples must be altered, causing significant energy to be splattered into adjacent channels.
Therefore, a method of effective peak-to-average ratio control without the generation of significant splatter is desired.